As the heritage industry, oiled by the National Lottery, cranks into top gear, is it too much to expect that the seamier side of our national past will be incorporated into the national record? The Transatlantic Slavery Gallery of the Merseyside Maritime Museum has pioneered the way with the world's first representation of the Other Holocaust, providing a model for uncovering a discreditable history.

There is no shortage of economic analyses of the consequences of the slave trade but these have been devoid of human content. A merit of Gretchen Gerzina's book is that she redresses the balance by reconstructing, as far as the evidence allows, the lives of some of those blacks, perhaps as many as 20,000, who came to England in the 18th century as seamen, children, slaves and servants, mostly brought over by returning planters or officials.

Many of these forced migrants were absorbed into English society through intermarriage although as the author shows graphically there was a vibrant black community in London, holding their own balls and concerts and contributing to the rumbustious life of the capital.

She has been able to build on Peter Fryer's indispensable Staying Power: the History of Black People in Britain (1984), and on the works of many others. Her account is an English, even a London story. Although provincial records have been little studied she does not refer to those that have been - for example Trevor Fawcett's work on Bath. Bristol and Liverpool, now slowly coming to terms with their slaving past, prompted in part by their communities' search for their own origins, only receive passing mention.

ÁñÁ«ÊÓƵ

What few black 18th-century accounts we have, are well used - the letters of Ignacio Sancho, the autobiography of Mary Prince and that of Olaudah Equiano, a best-seller in the 1790s and still in print, and which should be required reading in schools. However, much evidence has to come from outsiders.

Granville Sharp's papers are used to good effect to analyse the general issues raised by the moral and legal challenges to slavery, culminating in the Mansfield judgment, the misinterpretation of which is analysed in detail. The constant references to Jack Beef, the black servant of John Baker, solicitor general of St Kitts, in his cryptic diary gives a penetrating insight into life below stairs, the lot of many; but the trust placed in him by his master seems unique.

ÁñÁ«ÊÓƵ

There is a wealth of pictorial evidence of both high and low life from Reynolds and Gainsborough to Gillray and Cruikshank (many further examples could have been culled from Hugh Honour's The Image of the Black in Western Art, 1989). From the paintings of aristocratic groups with their black liveried servants has been chosen as dust jacket the puzzling Zoffany duet of Lady Elizabeth Finch Hatton and her black illegitimate cousin Elizabeth Dido Belle who lived for 30 years in Kenwood House and who was linked to the slavery issue by her great-uncle, the Duke of Mansfield.

Few Britons in the 18th century outside London and the seaports would have seen blacks, although from Fryer's evidence many must have had opportunities to admire the skill and exotic uniforms of the black trumpeters and drummers who were the pride of crack regiments. Where are the black trumpeters and drummers today?

By ending with emancipation the author avoids the question of why the black presence declines after the abolition of the slave trade and the shift in the focus of empire to the east. As it did so, England became less tolerant towards blacks, although already in the 1770s and 1780s we recognise fears familiar to the period after the arrival of the Windrush in 1948 - the need to save "the natural beauty of the Britons from the Morisco hue", to safeguard the jobs of English workers, and to prevent the threat of London "having the appearance of an Ethiopian colony". The influx of Loyalist veterans of the American war of independence increased the number of destitute blacks on London's streets, prompting Granville Sharp to propose their repatriation to Africa by the establishment of the colony of Sierra Leone - a foreshadowing of more recent repatriation proposals.

More insidious was the edge given to racism by the new "scientific" interpretations of racial differences. This was the other face of the Enlightenment, the passion for classification and hard fact which established a hierarchy of races, justified by zoology, phrenology, craniometry and the "facial angle". For all their cruelties and inconsistencies earlier attitudes had not been legitimated by reference to pseudo-science.

ÁñÁ«ÊÓƵ

With the current obsession over national identity this book deserves to be read so as to understand that the black presence in England stretches back centuries and that some white families (as is being discovered in the United States) may well have black ancestors. In one way or another, we are all mongrels and the sooner we accept it the better.

Alistair Hennessy is emeritus professor, University of Warwick where he was director, centre for Caribbean Studies.